April 1, 2000
by David A. Staples, BSc., DDS
Dentistry has done a remarkable job in providing excellent aesthetic, direct anterior restorations. We are now capable of doing similar for posterior teeth as well. The direct posterior composite has evolved now to the point where it not only looks good but functions well also. In fact, Gordon Christensen indicates that “CRA’s longstanding studies conducted for more than 10 years are showing a comparative acceptability to amalgam and Class II resins in small-to-moderate size restorations.”1
Dr. Christensen’s research is interesting since it was conducted on materials that existed as much as 10 years ago or more. Direct composite materials are undergoing continuous evolution and improvements with the result that today’s materials are better than those of even last year.
The direct posterior composite has now surpassed all other restorations that proceeded it when all aspects are considered. It is biocompatible, functional, minimally invasive, tooth reinforcing and esthetically pleasing.
The major stumbling blocks to most dentists in providing direct posterior composites as their primary restorations are technique sensitivity and increased time for placement of material. The principles of amalgam cavity design and restoration cannot be applied to the direct composite and expect it to perform properly. When they are applied they lead to sensitivity, open contacts, cracked cusps, unhappy patients and stressed dentists.
Adhesive dentistry using direct composites requires a whole new way of thinking. In other words a paradigm shift is required as virtually all that we were taught about cavity design and restorations in dental school must be unlearned.
The beauty of the bonded posterior composite is that it allows, at least in virgin teeth, the cavity preparation to be minimally invasive in its design. In dentistry we have traditionally viewed a service as being more valuable at least from a cost standpoint if it removed more tooth structure. Is it more valuable to a patient to have more tooth structure removed if they are planning to keep their teeth for a lifetime? After all many of our patients have multiple multi-surface amalgams in their mouths that are now breaking, have recurrent decay, or are in need of endodontic treatment, crowns, or all of the above.
Amalgam restoration requires mechanical retention. Sacrifice of sound tooth structure is needed for pins, post holes, or retentive grooves. Photoelastic studies demonstrate that retentive features act as stress concentrators when the restoration is under occlusal load.2 In contrast a bonded direct composite restoration saves more tooth structure. Stress is dissipated over rounded internal line angles and the entire surface area of the adhesive restoration is in full articulating function (unlike initially weak amalgam at placement).3
Unfortunately most if not all dentist were taught very little in the way of adhesive dentistry as it exists today while in dental school. The problem is that unlike amalgam, which have very few steps to placement the direct composite has multiple steps required for success where any one of which if done improperly results in failure. The result is that the technique sensitivity of direct composite restorations creates frustration due to tooth sensitivity and open contacts.
What about gold instead of amalgam — isn’t it the most superior restoration? Gold has a lot of positive attributes but for a 2 to 3 surface restoration it requires multiple visits — is therefore costly, requires a path of insertion- therefore is not minimally invasive, can’t be bonded without first tin-plating it and perhaps the biggest flaw is that to patients it doesn’t match the colour of their teeth.
Two clinical cases are illustrated. The first is a minimally invasive procedure on previously non-restored teeth and the second is an amalgam replacement with direct composite.
Case one (Figures 1 – 6) is an 18-year-old male who presented with carious lesions on the distal-proximal surface of tooth #46 and the mesial-proximal surface of #47.
Case one is presented to illustrate that the cavity design for the minimally invasive technique need only be what is necessary to remove decay and no more (Figure 4). Notice that there is no adherence to the principles necessary for amalgam placement.
Case Two is a 20-year-old male who presented with a failing amalgam restoration (see figure 8). This case illustrates that it is necessary to remove only the defective, pre-existing amalgam and carious tooth structure. Thin friable enamel must be removed but it is not necessary to remove undercut, or unsupported enamel due to the tooth strengthening features of the bonded composite restoration.4
1. Under rubber dam remove all defective restoration from tooth structure using a round-ended bur such as a 1557. You want to create rounded internal line angles.
2.Utilization of a caries indicating solution is necessary to insure that all decay is removed. (Figures 3 & 4)
3.If you are doing quadrant dentistry it is prudent to open one or two teeth at a time because the longer time necessary for placement of restorative material results in the unnecessary desiccation of the other open teeth in the quadrant.
4.Place a sectional matrix band (Palodent/Darway) and wedge followed by placement of a Bi-Tine ring (Draway) (Figures 5,10). The wedge should not be aggressively placed as tooth separation and therefore a positive contact will be provided by the Bi-Tine ring. The purpose of the wedge is merely to prevent inadvertent etching outside the prepared areas as well as the extrusion of material beyond the prep. Burnish the metal matrix against the adjacent tooth.
5.Clean the prep for 30 seconds using 2% chlorhexidene available commercially or through your local pharmacist and then rinse but do not air dry. Placement of the cavity cleanser may be unnecessary as any remaining micro-organism should be trapped in the polymerized resin preventing their access to “fuel” for their existence. It is done primarily as a matter of added security and the 2% chlorhexideine has been proven not to interfere with the bonding process.5
6.Etch enamel first for 5 seconds (Figure 10) and then apply etchant to dentin (Figure 11). Wait 10 more seconds and then thoroughly wash but again do not air-dry. Note the total etch time for enamel is 15 seconds while that of dentin is 10 seconds.
7.Apply a second antibacterial (Tubulicid Red, Global Dental) solution, which has residual action and also serves to re-moisten the dentin. Blot out any puddles that may exist but leave the dentin moist.
8.Apply the dentin and enamel adhesive. This can be done with either a 4th or 5th generation bonding system. Fourth generation bonding systems are those which have separate dentin and enamel bonding materials while in fifth generation systems they are combined. (See Table #1)
9.It is important to indicate that the use of bases and liners is no longer necessary and in some cases contraindicated. The reason being that the entire dentin surface is “hybridized” (or plasticized) using this technique. The hybridization process prevents the microorganisms from penetrating the dentinal tabules and thus the pulp chamber. The hybrid zone also prevents fluid flow around the odontoblastic process thus preventing normal physiological, post-operative sensitivity.6
10.Apply the 4th or 5th generation dentin bonding system for 15 to 30 seconds. Multiple coats are the preferred method. Lightly air dry to evaporate solvent in the dentin adhesive. Inspect the prep for a definitive sheen to the dentin.
11.If there are areas where the sheen is doubtful reapply the material. This is most likely to occur on deep-stained dentin. If you want to prevent post-operative sensitivity this step is absolutely necessary.
12.In the case of 4th generation materials a separate enamel bond is necessary. Apply the enamel bond but do not air thin as this incorporates air into the material resulting in uncured bond resin caused by oxygen inhibition. Instead remove any
excess bond resin with a brush (Benda Brush, Centrix). Light cure.
13.Place a flowable composite (Tetric Flow, Vivadent/Revolution, Kerr) to a depth of 1mm and light cure.
14.Next place a “heavy body” resin (Surefil, Dentsply/Caulk/Prodigy Condensable Kerr/P-60 3M, or Pyramid Bisco) to act as the dentin replacement material. This material is typically chosen to match the existing dentin shade usually A3 or A3.5.
15.The heavy body material is inserted as a bulk placement against both the buccal and lingual walls simultaneously prior to light curing. This is a departure from previous techniques because we’ve always been instructed to pack against one wall at a time until now. The new packable composites however have 50% less volumetric shrinkage compared to previous materials due to their high density and therefore cause less strain on tooth structure due to polymerization shrinkage.
16.The bulk placement using a heavy body composite can be done (assuming your light source is adequate) to a depth of 5.0mm. If the dentin replacement is to be greater than 5.0mm then it should be done in 2 steps.
17.The dentin replacement is done to 2mm short of the non-beveled, cavo-surface margin.
18.The final restorative material step is the enamel replacement. This is done with a translucent shade of material (Tetric Ceram Translucent, Ivoclar Vivadent).
19.Finish the restoration, adjust the occlusion and polish to a high shine.
Continuous change and improvement is the way of the future for direct posterior composites and adhesive dentistry. Each change in this area brings about an alteration in the way dentistry is practiced. As a result of this evolution/revolution in materials dentistry is moving from an age of amputation of tooth structure to an age of augmentation of tooth structure.
r. David Staples, BSc., DDS, is a 1984 graduate of the University of Western Ontario. He is also a Level I & II graduate of the Las Vegas Institute for Advanced Dental Studies. He maintains a private practice with emphasis on restorative esthetic dentistry in Barrie, ON.
Oral Health welcomes this original article.
1.Bonner, Phillip DDS. Dentistry at the turn of the Century: An Interview with Dr. Gordon Christensen; Dentistry Today, February 1999 Vol. 18. No.2:44-51.
2.Irvin A., Webb E., Holland G., et al Photoelastic analysis of stress induced from insertion of self threading retentive pins. J. Prosthetic Dent. 1985; 53:311-316.
3.Davis, Michael W. Amalgam Onlays: Outdated treatment for the new millennium. Dentistry Today August 1999; Vol. 18, No.8:42-47.
4.Hornbrook, David S. Pract. Perio Aesthetic Dentistry May 1996 Vol.8 No.4:59-65.
5.Cunningham P., Meiers J. The effect of dentin disinfectants on shear bond strengths of resin-modified glass ionomers. Quintessence Int. 1997; 28:545-551.
6.Leinfelder, Karl. Bases and Liners; To use or not to use. A paradigm shift. Dentistry Today February 1999 Vol.18, No.2:52.
7.Jackson R., New Posterior Resins Simplify Placement Technique; Oral Health, April 1999: 39-42.
|Fourth Generation Bonding Systems||Fifth Generation Bonding Systems|
|All Bond 2 (Bisco)||One Step (Bisco)|
|Clearfil Liner Bond (J Morita)||Prime & Bond 2.1(Dentsply Caulk)|
|Optibond Fl. (Kerr)||Optibond Solo(Kerr)|
|Scotch Bond Multi-Purpose Plus (3M)||Single Bond (3M)|